Earth-boring tools for forming wellbores in subterranean earth formations may include a plurality of cutting elements secured to a body. For example, fixed-cutter earth-boring rotary drill bits (“drag bits”) include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit. Similarly, roller cone earth-boring rotary drill bits may include cones that are mounted on bearing pins extending from legs of a bit body such that each cone is capable of rotating about the bearing pin on which it is mounted. A plurality of cutting elements may be mounted to each cone of the drill bit.
The cutting elements used in such earth-boring tools often include polycrystalline diamond compacts (“PDC”), which act as cutting faces of a polycrystalline diamond (“PCD”) material. PCD material is material that includes inter-bonded grains or crystals of diamond material. In other words, PCD material includes direct, inter-granular bonds between the grains or crystals of diamond material. The terms “grain” and “crystal” are used synonymously and interchangeably herein.
PDC cutting elements are generally formed by sintering and bonding together relatively small diamond (synthetic, natural or a combination) grains, termed “grit,” under conditions of high temperature and high pressure in the presence of a catalyst (e.g., cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer (e.g., a compact or “table”) of PCD material. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The supporting substrate may comprise a cermet material (i.e., a ceramic-metal composite material) such as, for example, cobalt-cemented tungsten carbide. In some instances, the PCD material may be formed on the cutting element, for example, during the HTHP process. In such instances, catalyst material (e.g., cobalt) in the supporting substrate may be “swept” into the diamond grains during sintering and serve as a catalyst material for forming the diamond table from the diamond grains. Powdered catalyst material may also be mixed with the diamond grains prior to sintering the grains together in an HTHP process.
Upon formation of the diamond table using an HTHP process, catalyst material may remain in interstitial spaces between the inter-bonded grains of the PDC. The presence of the catalyst material in the PDC may contribute to thermal damage in the PDC when the PDC cutting element is heated during use due to friction at the contact point between the cutting element and the formation. Accordingly, the catalyst material (e.g., cobalt) may be leached out of the interstitial spaces using, for example, an acid or combination of acids (e.g., aqua regia). Substantially all of the catalyst material may be removed from the PDC, or catalyst material may be removed from only a portion thereof, for example, from a cutting face of the PDC, from a side of the PDC, or both, to a desired depth. However, a fully leached PDC is relatively more brittle and vulnerable to shear, compressive, and tensile stresses than is a non-leached PDC. In addition, it is difficult to secure a completely leached PDC to a supporting substrate.
To improve the thermal stability, the mechanical durability, and bonding characteristics of the PDC, nanoparticles (e.g., particles having an average particle diameter of about 500 nm or less) may be provided in the interstitial spaces of the PDC. However, disadvantageously, as higher concentrations of nanoparticles are incorporated into the interstitial spaces, the “sweep” of catalyst material from the supporting substrate during subsequent HTHP processing is inhibited, resulting in formation of a nanoparticle-enhanced (“nanoparticle-enhanced”) PDC that may be poorly sintered at positions distal from an interface of the nanoparticle-enhanced PDC and the supporting substrate.